Secondary emission multiplier



9, M. QANEHAGEN Filed Aug. 29. 1940 Patented Dec. 9, 1941 SECONDARY EMISSION MULTIPLIER Max Sandhagen, Berlin-Zehlendorf, Germany,

assignor to Fernseh G. in. b. H., Berlin-Zehlendorf, Germany Application August 29, 1940, Serial No. 354,739 4 InGermany September 19, 1939 8 Claims.

This invention relates to secondary emission multipliers and in particular to the type of multiplier in which a number of secondary emission electrodes in the form of grids or nets are arranged transversely to the main path of the electrons. The plane of the grids in such multipliers is usually substantially perpendicular to the main discharge path.

It is an object of the invention to provide a multiplier having a high output current. It is a further object to overcome the difliculties which are produced by high current densities in the last multiplier stages resulting in high temperatures of the output electrodes. These high tempera tures must be avoided because the emitting layers of the secondary emissive electrodes are very sensitive to high temperatures and lose their emissive properties. It is a further object to provide a multiplier having a linear amplification which is not changed by space charges between the electrodes.

A further object is to improve the form of multipliers in which the grid electrodes have increasing surfaces in progressive stages so that a larger surface is present for taking up the larger current. The concentric arrangements which have been suggested for this purpose are very difficult to construct because, the practice with contrary to ordinary amplifier tubes, grids of a very close mesh must be used.

According to the invention at least a part of the secondary emissive electrodes is curved concavely towards the cathode, the radius of curvature of the electrodes being substantially equal for all the curved electrodes. The centres of the curved electrodes are not coincident but are shifted from stage to stage in the direction of the electron current. This arrangement has the effect that the electron current is distributed from stage to stage over a wider surface because the strength of the electric field increases from the axis of the arrangement in the direction towards the edge. This electrode arrangement fits easily into a cylindrical bulb having a spherical end portion. The tube of the invention must be distinguished from multipliers having grid electrodes curved convexly towards the cathode in order to produce a concentrating effect upon the electrons.

Other aspects of my invention will be apparent or will be specifically pointed out in the description forming a part of this specification, but I do not limit myself to the embodiment of the invention herein described, as various forms may be adopted within the scope of the claims.

Referring to the drawing the single figure shows a longitudinal cross-section through a multiplier according to the invention.

The envelope 1 consisting, for example, of glass carries on a presser foot a cathode 2, a control grid 3 and an accelerating electrode 4. This system is used for producing the primary electrons. A shield electrode 5 surrounds this electrode arrangement and deflects the primary electrons in the direction of the axis of the tube towards the first secondary emissive grid 6. The multiplying arrangement consists of a number of spherically curved grids 6 the centres of curvature of which however do not coincide. The radius of curvature is the same for all the grids. The centres of curvature are shifted in the direction of the electron current and of increasing potentials of the electrodes. The multiplier system is limited by a conical surface within which the electrodes 5 are impacted by electrons approximately uniformly over their entire surfaces. The lines 1 represent the path of electrons emitted near the edge of the first grid. These paths show that the electrons are drawn outwardly from stage to stage so that the total surface of the electrodes impacted by the electrons is increased from stage to stage. The last secondary emissive electrode is a metallic layer 8 upon the wall of the tube I, while the output electrode 9 has the form of a grid of wide mesh, situated between the electrode 8 and the last electrode 6. This arrangement has the advantage that the electrode 8 can be easily and intensively cooled from the outside of the tube.

The arrangement can be modified by inserting between the system for producing the primary electrons and the electrodes 6 one or a number of plane secondary emissive electrodes. The arrangement can further be modified by using cylindrically curved electrodes instead of the spherically curved electrodes. The grids can also be replaced by foils adapted to emit electrons from the side directed away from the impacted side.

The spherically curved electrodes are preferably made all with one and the same forming tool because they have all the same radius of curvature.

Th invention is not limited to the special construction shown in the figure. It can be used in connection with a photoelectric cathode or with input and control systems of different design.

What I claim is:

1. Secondary emission multiplier including a cylindrical acceleration grid mountedwith the axis of the cylindrical grids in alinement with the main dscharge path of said secondary emissive electrodes.

2. Secondary emission multipler including" in an evacuated envelope a sourcei bf lelectronsaa plurality of foraminous s'econdary emissive electrodes mounted one behind the other transversely to the main discharge,,-path,-?said:::electrodes having a concave curvatureiatowards-isaid source of electrons, said source of electrons including a cathode, a cylindrical controlgridand' a cylindrical acceleration grid mounted with the axis of the cylindrical grids in alinement with the main discharge path of said secondary emissive electrodes. and a negative shield elec- 5 trode surrounding said source of electrons and having an opening in the direction of said secondary emissive electrodes. I

t 3: Secondary emission multiplier including in an evacuated envelope a plurality of foraminous 'secondary emissive electrodes mounted one be- .hi-nd-rt-he-,othertransversely to the main discharge path, said electrodes having a concave curvature towards the source of electrons, the radius-jotcurvature being substantially the same 15 for allsa'id "electrodes, and a secondary emissive eelectrode in the-form of a wall coating covering the part -of 'said envelope situated in the direction of the main discharge path.

MAX SANDI-IAGEN. 

